Conventionally, hydrotalcites, hydrous bismuth oxide, hydrous magnesium oxide, hydrous aluminum oxide, etc. have been known as inorganic anion exchangers.
Among them, bismuth compounds have been known as inorganic anion exchangers for a long time. Bi6O6(OH)x(NO3)6−x.nH2O (x is 3.5≦x≦5.5, and n is 0 or a positive number; for example, see Patent Document 1), and Bi10O13+x(NO3)4−2x(x is −0.18≦x≦0.29; for example, see Patent Document 2) have been proposed as bismuth compounds having high ion exchange performance.
The inorganic anion exchanger is mixed with resins for electronic component encapsulation, resins for electrical component encapsulation, resins for electrical products, etc.
For example, many of LSIs, ICs, hybrid ICs, transistors, diodes, thyristors, and hybrid components thereof are encapsulated using epoxy resins. There has been a demand that such an electronic component encapsulating material does not cause any defect attributed to ionic impurities in a raw material or moisture that invades from the outside. In addition, there has been a demand that the electronic component encapsulating material has various characteristics including flame resistance, high adhesion, crack resistance, and electrical properties such as high volume resistivity.
Epoxy resins often used as electronic component encapsulating materials are mainly composed of an epoxy compound, and also include an epoxy compound curing agent, a cure accelerator, an inorganic filler, a flame retardant, a pigment, a silane coupling agent, etc.
Further, recent higher integration of semiconductors has brought about earlier generation of corrosion of aluminum due to reduction of the aluminum interconnect width on IC chips. This corrosion is promoted mainly by moisture invading an epoxy resin used as an encapsulating material. Since more heat is generated upon use of the semiconductor due to the reduction of the interconnect width, a large amount of a flame retardant such as antimony oxide, a brominated epoxy resin and an inorganic hydroxide is added to the epoxy resin, thereby further promoting corrosion of interconnects made of aluminum or the like.
In order to prevent the above-mentioned corrosion, further improvement in moisture resistance reliability of epoxy resins has been demanded. In order to meet this demand for the improvement in moisture resistance reliability, it has been already proposed that a hydrotalcite that is an inorganic anion exchanger be mixed with the epoxy resin or the like to capture impurity ions that cause problems, especially, halogen ions (for example, see Patent Document 3, Patent Document 4, Patent Document 5, and Patent Document 6, etc.).
Since this compound already has anions such as hydroxide ions and carbonate ions, its anion exchange performance cannot be said sufficient.
When this hydrotalcite compound is calcinated, the anions within its structure are eliminated and a calcined product of a hydrotalcite is obtained. Since this calcined product includes no anion therein, the calcined product has excellent anion exchange performance compared with the hydrotalcite compound. This calcined product restores the layered structure, when absorbing water.
It has been also proposed that this calcined product of the hydrotalcite is mixed with an epoxy resin, etc. (for example, see Patent Document 7). The obtained mixture has excellent anion exchange performance, and effectively improves the moisture resistance reliability of electronic components. On the other hand, since the obtained mixture has very high moisture absorbency and easily absorbs moisture in the air, the obtained mixture absorbs moisture in electronic components, and a volume of the mixture increases with this moisture absorption. Accordingly, when the mixture is exposed to a high temperature in processes in a solder bath, a reflow apparatus, etc., coming off may be generated between insert items, such as a component and a lead frame, and a molding material for encapsulation, due to thermal stress caused by a difference in thermal expansion coefficient of a substrate, etc., or due to vapor pressure generated by vaporization of the absorbed moisture. This coming off may cause cracks in packages, damages of chips, or the like.
An epoxy resin composition for semiconductor encapsulation has been known (for example, see Patent Document 9), in which an oxyacid bismuth oxyhydroxide compound that is an anion exchanger (for example, see Patent Document 8) is blended.
Generally, anion exchangers adsorb anions well when their surrounding environment is acidic, but it is difficult for anion exchangers to adsorb anions when their surrounding environment is around neutral or alkaline. Depending on an additive mixed with the encapsulating material, the pH of the resin composition may become around neutral so that the effect of the anion exchanger may not be sufficiently exhibited.
As a countermeasure against this, a method has been proposed in which a cation exchanger that is a solid acid is mixed with the anion exchanger to reduce an apparent pH so that the mixture can be used with improved ion exchange properties (for example, see Patent Document 10). However, when the solid acid is added to a resin, physical properties of the resin may be impaired. Additionally, cation exchangers often include heavy metals. Recently, use of such cation exchangers in combination may be prohibited due to environmental consideration.
An epoxy resin used for a printed wiring board has been known, in which an inorganic ion exchanger, such as a cation exchanger, anion exchanger and amphoteric ion exchanger, is mixed (for example, see Patent Document 11).
A printed circuit board containing an epoxy resin or a polyphenylene oxide resin together with an ion scavenger in aramid fibers has been known. As this ion scavenger, an ion exchange resin and an inorganic ion exchanger are exemplified, and as the inorganic ion exchanger, an antimony-bismuth-based one and a zirconium-based one are described (for example, see Patent Document 12).
An insulating varnish containing an ion scavenger has been known, and a multi-layered printed wiring board is produced using this insulating varnish. As this ion scavenger, activated carbon, zeolite, silica gel, activated alumina, activated clay, hydrated antimony pentoxide, zirconium phosphate, hydrotalcites, etc. are exemplified (for example, see Patent Document 13).
An adhesive film for multi-layered interconnection boards, with which an inorganic ion adsorbent is mixed, has been known. As this inorganic ion adsorbent, activated carbon, zeolite, silica gel, activated alumina, activated clay, hydrated antimony pentoxide, zirconium phosphate, hydrotalcite, etc. are exemplified (for example, see Patent Document 14).
An epoxy resin adhesive containing an ion trap agent has been known. An anion exchanger or a cation exchanger is exemplified as this ion trap agent (for example, see Patent Document 15).
A conductive epoxy resin paste containing an ion scavenger, silver powders and so on has been known. As this ion scavenger, hydrated bismuth nitrate, magnesium aluminum hydrotalcite, antimony oxide, etc. are exemplified (for example, see Patent Document 16).
The hydrotalcites mentioned as an ion exchanger and an ion scavenger in the above-mentioned known examples are used as they are, or as a calcined body.
Among these, hydrotalcites and hydrous bismuth oxide have high anion exchangeability, and comparatively excellent chemical resistance and thermal resistance, and therefore, are used for various applications. For example, in the field of electronic industry, they are blended with encapsulating resins for semiconductors, and used in order to improve reliability of semiconductor components, etc.
However, hydrotalcites are highly soluble under high temperature and high humidity conditions, such as in hot water at not less than 100° C. Moreover, since hydrotalcites are so high in moisture absorbency as to give an adverse influence on physical properties of encapsulating resins, the range of application of hydrotalcites is limited.
On the other hand, bismuth compounds such as hydrous bismuth oxide have excellent anion exchange performance and have been applicable in a wider range. However, in order to cope with further reduction of aluminum interconnect width in IC chips in recent years and the resulting generation of heat, a material of high performance having higher ion exchangeability, higher thermal resistance and so on has been demanded, and there have been applications for which conventional bismuth compounds cannot be used.    Patent Document 1: Japanese Patent Laid-Open (Kokai) No. 63-60112    Patent Document 2: Japanese Patent Laid-Open (Kokai) No. 07-267643    Patent Document 3: Japanese Patent Laid-Open (Kokai) No. 63-252451    Patent Document 4: Japanese Patent Laid-Open (Kokai) No. 64-64243    Patent Document 5: Japanese Patent Laid-Open (Kokai) No. 60-40124    Patent Document 6: Japanese Patent Laid-Open (Kokai) No. 2000-226438    Patent Document 7: Japanese Patent Laid-Open (Kokai) No. 60-42418    Patent Document 8: Japanese Patent Laid-Open (Kokai) No. 02-293325    Patent Document 9: Japanese Patent Laid-Open (Kokai) No. 02-294354    Patent Document 10: Japanese Patent Laid-Open (Kokai) No. 60-23901    Patent Document 11: Japanese Patent Laid-Open (Kokai) No. 05-140419    Patent Document 12: Japanese Patent Laid-Open (Kokai) No. 09-314758    Patent Document 13: Japanese Patent Laid-Open (Kokai) No. 10-287830    Patent Document 14: Japanese Patent Laid-Open (Kokai) No. 10-330696    Patent Document 15: Japanese Patent Laid-Open (Kokai) No. 10-013011    Patent Document 16: Japanese Patent Laid-Open (Kokai) No. 10-007763